The invention relates to a dual circuit brake valve system for a vehicle brake system actuated by compressed air or the like.
A dual circuit brake valve system of this type is known from DE 34 39 086 A1.
In the known brake valve system a compression spring is provided between a first piston, which serves to control the pressure in the first brake circuit, and a second piston, which serves to control the pressure in the second brake circuit, whereby the second piston is actively connected to the first piston via said compression spring. When the first piston moves in the direction of a first combined inlet and outlet valve of the valve arrangement, the second piston is also moved in the direction of a second combined inlet and outlet valve of the valve arrangement. When the valve arrangement is actuated, the interaction between the two pistons via the compression spring compensates to the greatest possible extent for the friction caused by the sealing rings on the second piston and the force of a spring acting upon the valve body of the second combined inlet and outlet valve. Thanks to this measure, the second piston is able to react more rapidly to the control pressure to which it is subjected so that a nearly simultaneous actuation of the two combined inlet and outlet valves is possible. The evolution of the pressure selected by the valve arrangement is identical for the entire pressure evolution in the first brake circuit and in the second brake circuit. The difference between the pressure in the first brake circuit and in the second brake circuit is constant for the entire pressure rise.
In order to avoid uneven wear of the brake linings of the wheels of a vehicle, the pressure difference .DELTA.p is kept as close to zero as possible.
A brake valve arrangement of the type mentioned initially is especially well-suited for vehicles with a dual circuit brake system in which the two circuits are operated with equally high pressure.
However, this known brake valve arrangement is not suitable for all dual circuit brake systems. In particular, in this known brake valve arrangement, pressures of equal force are injected into both brake circuits. This is not desirable in dual circuit brake systems wherein the pressure supplied to each of brake circuits is regulated as a function of the load.
It is the object of the instant invention to improve the known dual circuit brake valve installation in such manner that for an overall pressure increase in a braking process, the evolution of pressure in the second brake circuit is identical or nearly identical with the pressure evolution in the first brake circuit, and when the pressure is below a predetermined level, the pressure difference .DELTA.p between the pressure in the first brake circuit and in the second brake circuit is less than the pressure difference .DELTA.p after this predetermined pressure level has been exceeded in both brake circuits.